Kansas Geological Survey, Current Research in Earth Sciences, Bulletin 244, part 1
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Pteranodon

The utility of this method for inferring stratigraphic position from locality data was examined with the pterosaur Pteranodon. Pteranodon was a large pterosaur with a wingspan ranging from 3 m to 6 m (9 ft to 20 ft). Known from roughly 1,200 specimens, it was an important part of the fauna of the Western Interior Seaway and was the most common tetrapod after the mosasaurs Platecarpus, Clidastes, and Tylosaurus. The postcranial skeleton is of no taxonomic value at the species level, and although Pteranodon occurs in two size classes, this reflects sexual dimorphism in size rather than specific differences (Bennett, 1991, 1992). The skull, on the other hand, has been used to distinguish species. Five nominal species of Pteranodon are based on skulls, and they differ in the size and shape of the cranial crest and the angle between the occiput and the palate. The type skulls of Pteranodon longiceps, P. marshi, and P. eatoni have a reclined occiput that is plesiomorphic for pterodactyloids, while those of P. sternbergi and P. walkeri have a more upright occiput. In the absence of stratigraphic information, it was hypothesized that the cranial morphology evolved from a reclined occiput to an upright occiput, and that a single species or lineage of Pteranodon was present in the Smoky Hill Chalk Member. If this were the case, one would not expect the two morphologies to co-occur, and skulls with reclined occiputs should be stratigraphically lower than those with upright occiputs.

To test this hypothesis, it was necessary to determine the stratigraphic positions of the type skulls. The localities of these specimens of Pteranodon, as well as nearby outcrops, were visited and stratigraphic columns measured. Localities in Logan and Gove counties are shown in fig. 1, and the stratigraphic columns are listed in the Appendix. These columns were then compared to the composite stratigraphic column of Hattin (1982), and stratigraphic positions of the outcrops were determined. Using the stratigraphic columns and any other available information about the position or locality of the specimens, it was possible to determine the stratigraphic position or range for these type specimens of Pteranodon. The five nominal species are discussed below in the order in which they were named.

Fig. 1--Map of Logan and Gove counties, Kansas, showing the localities where stratigraphic columns were measured. Red lines between localities show their order in figs. 2 and 5, 6, 7.

Pteranodon longiceps (YPM 1177)--This skull was collected May 2, 1876, by S. W. Williston. Williston's 1876 field notebook in the YPM archives lists the locality as "3 mi. NE of Monument Rocks in fine yellow chalk," and a map prepared by S. W. Williston (also in the YPM archives) shows that the specimen was collected on the west side of the first drainage east of Monument Rocks and about 3 mi (4.8 km) north of the Smoky Hill River. This is in Gove County, not in Wallace or Logan, and is approximately Locality 72. Comparison of this locality with Locality 37 to the southwest and Localities 33 and 35 to the northeast shows that Locality 72 ranges from 4 m (13 ft) below Marker Unit 15 up almost to Marker Unit 16 (fig. 2). At Locality 72, the chalk is gray from 1.5 m (5 ft) above Marker Unit 15. The fact that the skull was collected in yellow chalk while the chalk in the lower parts of the exposure is gray suggests that the skull came from at least 2 m (6.5 ft) above Marker Unit 15 and below Marker Unit 16.

Fig. 2--Correlation of stratigraphic columns of localities in western Gove County, Kansas. Black bands indicate bentonites, seams, and in a few instances a change in lithology; white indicates chalk. Localities are numbered across the top and arranged in order from west to east. The unnumbered column at right is the composite stratigraphic column from Hattin (1982). Hattin's marker units are identified by the numbers at right, and Russell's (1929) marker unit H is also indicated. The relative vertical position of different stratigraphic columns in the figure is not significant. The arrow by Locality 72 indicates the change from gray to yellow chalk.

Pteranodon sternbergi (FHSM VP 339)--This skull was collected by G. F. Sternberg from sec. 12, T. 8 S., R. 22 W., Graham County, Kansas, about 1 mi. (1.6 km) west of Bogue and between Highway 24 and the south fork of the Solomon River (Bardack, l965). An outcrop in the NE sec. 12, T. 8 S., R. 22 W., Graham County, is very small and difficult to measure, but it has abundant remains of Inoceramus (Volviceramus) grandis. The presence of I. (V.) grandis indicates that the specimen of P. sternbergi is from Stewart's (1988) Biostratigraphic Zone A or B and quite low in the Smoky Hill Chalk Member. Marker Unit 4 is visible near the top of the approximately 8 m (26 ft) of exposure and also is exposed in other nearby outcrops. Although the exact horizon of the type skull is unknown, it must have come from approximately Marker Unit 4 or a short distance below.

Pteranodon marshi (YPM 2594)--This skull was collected July 20, 1877, by S. W. Williston from "near Smoky Hill River, Wallace Co." (according to field labels and YPM catalog). A chronological listing of all specimens collected by the field party indicates that they had been moving east from Russell Springs for a number of weeks and collected a mosasaur on Plum Creek in western Gove County, also on July 20. The skull was presumably collected somewhere near there. Localities 33, 35, and 42 are on either side of Plum Creek and indicate that exposures on Plum Creek are between Marker Units 16 and 19 (fig. 2). Therefore, the skull was probably collected between those marker units.

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